Nozzle for coating an article with a liquid substantially free from discrete immiscible matter removed by velocity gradient separation



1970 D. B. CHENOWETH ETAL 3,525,998

NOZZLE FOR COATING AN ARTICLE WITH A LIQUID SUBSTANTIALLY FREE FROMDISCRETE IMMISCIBLE MATTER REMOVED BY VELOCITY GRADIENT SEPARATIONOriginal Filed Jan. 16, 1967 2 Sheets-$heet l DEAN B. CHENOWETH RICHARDLOUIS BARNARD INVENTORS ATTORNEYS Aug. 25, 1970 cHENQwETH ET AL3,525,998

NOZZLE FOR COATING AN ARTICLE WITH A LIQUID SUBSTANTIALLY FREE FROMDISCRETE IMMISCIBLE MATTER REMOVED BY VELOCITY GRADIENT SEPARATIONOriginal Filed Jan. 16, 1967 2 Sh eets Sheet 2 1 I Ill/Ill ll [/17 DEANB. CHENOWETH RICHARD LOUIS BARNARD INVENTORS I I. FIG.9 U 1 ATTORNEYSUnited States Patent 3,525,998 NOZZLE FOR COATING AN ARTICLE WITH ALIQUID SUBSTANTIALLY FREE FROM DIS- CRETE IMMISCIBLE MATTER REMOVED BYVELOCITY GRADIENT SEPARATION Dean B. Chenoweth, Minneapolis, and RichardL.

Barnard, Wayzata, Minn., assignors, by mesne assignments, to EastmanKodak Company Application Jan. 16, 1967, Ser. No. 627,279, which is adivision of application Ser. No. 259,707, Feb. 19, 1963, now Patent No.3,299,195, dated Jan. 17, 1967, which in turn is a continuation-in-partof application Ser. No. 178,128, Mar. 7, 1962. Divided and thisapplication May 27, 1969, Ser. No. 828,400

Int. Cl. B05b 1/04 U.S. Cl. 239-597 3 Claims ABSTRACT OF THE DISCLOSUREApparatus and method for curtain coating and also an article coated witha composition free of contaminating particles and/ or bubbles. Theapparatus includes means for removing contaminants and means, such as anozzle, for projecting a falling curtain of a viscous liquid coatingcomposition and may include as additional elements a conveying means foran article to be coated, a catch basin for that portion of the fallingcurtain not used for coating, a reservoir, and a pump. Contaminatingparticles and/or bubbles are removed from the coating composition whileit is in the form of a viscous liquid by propelling the contaminatedliquid in laminar flow through an outer conduit in which a smallerconcentric inner conduit is located having an open end facing the flowof liquid whereby contaminating particles in the contaminated liquidmove as a result of velocity gradient separation toward the center ofthe flowing liquid and are removed through the inner conduit.Preferably, the capacity of the inner conduit is in the range of from toW the capacity of the outer conduit and extends through the wall of theouter conduit at a point downstream from the inner opening of the innerconduit, the capacity of the downstream portion of the outer conduittogether with the capacity of the inner conduit being substantiallyequal.

This application is a division of Chenoweth et al. U.S. Ser. No.627,279, filed Jan. 16, 1967, which is a division of U.S. Ser. No.259,707, filed Feb. 19, 1963, now Pat. No. 3,299,195, issued Jan. 17,1967, Ser. No. 259,707 being in turn a continuation-in-part of U.S. Ser.No. 178,128, filed Mar. 7, 1962, now abandoned.

This invention relates to and provides a new and unusual method andapparatus for separating, from a mass of liquid, liquid carryingdiscrete immiscible matter and disclosed in an exemplary use withrespect to removing entrained bubbles of gas, such as air, vapor and thelike, from liquids, including viscous liquids such as molten syntheticresins, by velocity gradient separation, to yield substantiallybubble-free liquids, the coating method thereby made feasible and acoated article produced thereby.

The method of this invention contemplates the propelling of a liquid ina column to establish a linear flow known as laminar flow, retarding theliquid flow adjacent the periphery of the column to cause entrainedimmiscible matter such as bubbles, and particularly visible bubbles ofentrained gas, to move toward the center of the column, either once, orprogressively, to remove at least the major portion of said entrainedgas bubbles, and preferably to remove all bubbles according to visualinspection.

Specifically, the structure for extracting gas bubbles from the liquidin which they are entrained includes at 3,525,998 Patented Aug. 25, 1970least one set of tubular conduits, one of which is smaller than andsubstantially concentrically positioned within the other and receivesthe liquid with the entrained bubbles as a result, it is thought, oftheir being concentrated according to the velocity gradient of theliquid flow within the larger tubular conduit in a relatively highspeed, low shear area of flow near the center of the larger conduitwhile the peripheral portion of the liquid is slowed down and maintainedat a higher shear stress as the result of friction between the liquidand the outer of the two tubes.

This invention also provides a clear film projecting apparatus includingone or more velocity gradient bubble removing means and may include anozzle having means for discharging residual bubble carrying liquid atspaced points in contact with the sides of a discharge film from whichbubbles have been removed to serve as a means for holding this curtainor film is a stretched condition for a majority of its extension to acoating area. The struc ture of he invention also affords choke controlmeans which permits maximum flow of clear liquid consistent withefficient bubble removal.

The invention also provides novel coated articles including an articlecompletely encapsulated in a seamless unbroken film and an article on abacking board secured to the backing board by having similar unbrokenseamless film adhered to the board and covering the article on the sidespaced from the board surface on which it rests. These films arecommonly and preferably clear. These coated articles and the method forproducing them is dependent on and made possible by the velocitygradient separation and film projecting apparatus described above. Themethod consists of projecting a film that is substantially wider thanthe article to be encapsulated or the board supporting the article to becovered and passing the same through the film while it is beingprojected. This may be done by any suitable powered or gravity conveyorselected from numerous conventional types available and which form partof this invention only in combination with other structure as defined inthe claims hereafter.

It has been proposed before to project or provide a thin curtain of acoating material for covering objects to be passed through the curtainand over which an even film of the material is deposited. One of themajor shortcomings of all previously suggested methods and structures,however, has been their inability to efficiently remove bubbles from thecoating material or liquid to provide a substantially clear orhomogeneous curtain or film of the material to be used as a commerciallysuccessful coating.

When using conventional bubble removing apparatus, the problem ofremoving entrained gas, principally air and other fluid vapor bubbles,from any fluid material or liquid coating, is even greater when oneattempts to deal with extremely viscous materials such as moltenpolyethylene and similar fluid synthetic resinous materials or plastics.The nature of these viscous materials is such that bubbles created inthem do not rise to the surface even slowly as they do in many of theliquids from which it is desired to remove bubbles but remain trapped inthe fluid plastics almost indefinitely. This problem of entrained gas inthe molten or fluid plastics was one which provided a very seriousproblem from the standpoint of providing a substantially clear orbubble-free (and therefore strong even though thin) curtain of theliquid material, usually including recirculated waste, until the presentinvention was made. Prior to discovering the present method andapparatus for removing bubbles, all of the previously suggested methodsand structures were unsuccessful commercially, at least in use with veryviscous liquids, as were the articles produced thereby. While a numberof them would either minimize creation of bubbles or remove bubbles fromthe 3 material to some degree there was always a serious problemremaining so that none of them were commercially or practicallysuccessful.

In projecting a film of molten plastic, for example, onto an object tobe coated, any gas or vapor bubbles produce at least two undesirableeffects. One problem is that the visibility through the film is reducedwhich makes it a commercially unsatisfactory package cover, because theobject packaged is obscured by the milky condition of the plastic withentrained gas. The second and much more serious problem is that a verythin or weak spot in the film is produced which materially reduces thestrength of the film so that it may rupture upon the shrinkage of themolten film as it hardens, or when subject to stress.

The method and apparatus of this invention has been found highlysatisfactory in the removal of entrained gas bubbles, from viscousmaterial in the range of 5000- 20,000 centipoises and perhaps evengreater viscosities. It has been discovered that liquids of lesserviscosity require a greater linear velocity for maximum separation andpreferably a series of separations. It has been found that when fluid,particularly viscous fluid, is forced to flow linearly through anunobstructed tube with a minimum of turbulence, a velocity gradient isestablished by retardation of the flow at the periphery of the columnthrough contact with the wall of the conduit. Thus, a velocity gradientis established in the form of a forwardly projecting conical or bulletcross section in the liquid. Gas bubbles, and particularly the largerones, move to the center of the column of the liquid or to the portionbehind the apex of the cone or behind the nose of the bullet and may bestripped out from this area of least shear by a concentric strippingtube. This concentration is emphasized as the viscosity increases. It isimportant to maintain the columnar flow with a minimum of turbulence.

Accordingly, it is an object of this invention to provide a method andapparatus for the removal of entrained gas bubbles from liquid in aconduit by velocity gradient separation.

It is yet another object of this invention to provide a means forremoving entrained gas bubbles from liquids that is extremely compactand requires almost no space to be incorporated into other structure.

It is a still further object of this invention to provide a device ofthis nature which can be adjusted for the viscosity of the materialbeing used.

A further object of this invention resides in providing a new and usefulmethod or process for removing entrained gas bubbles from liquid.

Still a further object of this invention resides in a new and usefulmethod or process for providing a substantially bubble-free liquid film.

It is a further object of this invention to provide a new and usefulfilm coated article and process and coating device that projects a filmsubstantially and consistently free from entrained bubbles.

A further object of this invention is to provide a coating structurethat has a separating means having no parts that move while removal ofentrained gas bubbles is taking place.

It is another object of this invention to provide a novel coated articleconsisting of an article encapsulated in a seamless, unbroken clearfilm.

Another object of this invention is to provide a novel coated articleconsisting of a treated backing board, an object to be packaged and aclear, unbroken film covering the object and sealed to said backingboard.

Yet another object of this invention is to provide a cur tain coatingapparatus that recirculates fluids of viscosities of 5000 centipoisesand more, yet provides a bubble-free curtain.

A further object of this invention resides in the provision of a methodwhereby columns of residual bubble containing material are used tomaintain in generally planar extension a film from which the bubbleshave been removed.

Other and further objects of the invention reside in the specificstructural features of the apparatus including the primary bubbleextracting or separating means, the secondary separating means, thecontrol of the flow therefor, the film generating structure associatedtherewith, and cooperation between the separating means and the filmgenerating nozzle.

Still other and further objects of the invention reside in theparticular method steps for providing a liquid from which bubbles havebeen substantially removed.

Other and further objects of the invention are those inherent andapparent in the apparatus as described, pictured and claimed.

To the accomplishment of the foregoing and related ends, this inventionthen comprises the features hereinafter fully described and particularlypointed out in the claims, the following description setting forth indetail certain illustrative embodiments of the invention, these beingindicative, however, of but a few of the various ways in which theprinciples of the invention may be employed.

The invention will be described with reference to the drawings in whichcorresponding numerals refer to the same parts and in which:

FIG. 1 is a partial front elevation, partial vertical section of a filmor curtain projecting nozzle structure or apparatus embodying thepresent invention with broken lines illustrating hidden parts;

FIG. 2 is a partial plan view, partial horizontal section of theapparatus of FIG. 1 with hidden parts illustrated with broken lines;

FIG. 3 is a vertical section taken on the line 3-3 of FIG. 2; brokenlines illustrate hidden parts;

FIG. 4 is a diagrammatic representation of an entire film generatingsystem employing the film or curtain projecting apparatus of FIGS. 1-3with broken lines illustrating a bubble entrained column of curtainmaterial and hidden parts;

FIG. 5 is a fragmentary diagrammatic view showing an advanced positionof an article to be coated, as it passes through the curtain of FIG. 4;

FIG. 6 is a view substantially identical to FIG. 5 but illustrating astill further advanced position of an article that has passed throughand been coated by the curtain of FIG. 4;

FIG. 7 is a front elevational view of the bottom part of the nozzle ofthe curtain or film projecting apparatus showing the curtain projectedtherefrom;

FIG. 8 is a fragmentary sectional view of a modified form of structureof the instant invention; and

FIG. 9 is a composite view of the bottom part of the nozzle, a filmprotected thereby, an article approaching the curtain and theencapsulated article after having passed through the curtain; thearticle shown approaching the curtain is shown in fragment to conservespace and the scale used in that of FIGS. 4, 5 and 6.

Reference is now made to the drawings and first to FIG. 4. The system isshown as comprising generally a reservoir 10 for containing fluid orcoating material connected by a supply pipe or conduit 11 to a suitablepump 12. A discharge pipe or conduit 14 extends from the pump to a mainor primary velocity gradient separator or bubble separating meansgenerally designated 15. From this unit the separated or removed liquidwith entrained bubbles enters the return pipe 16 and is discharged backinto the reservoir 10. Another pipe 17 carrying liquid from which mostof the entrained bubbles have been removed extends to a nozzle meansincluding a secondary velocity gradient separator 18. Of course, it isto be understood that while it is preferred to re-use and re-circulatethe bubble-containing liquid which is removed, it is not necessary ifcost is not considered. In such instance, pipe 16 (as well as pipe 24)can be connected to a waste receptacle.

From the nozzle means 18 a curtain or film 19 is projected downwardbetween two suitable conveyors 20 and 21, which, as shown, are beltconveyors and have their top belt runs moving in the direction of thearrows. Between and below the two conveyors is the excess liquid or filmmaterial catch basin 22. It is connected by a suitable pipe such as 24to the reservoir 10 so that any excess material may be returned to thereservoir for re-use normally or discarded as noted above.

As shown in FIG. 7, and as later explained in more detail, the film orcurtain 19 projected by nozzle means 18 actually consists of a centerfilm portion 25 from which bubbles have been removed, and usually clear.engaged at each side by a column 26 of the same liquid having theresidual entrained air or gas bubbles 27. Usually the column 26 has somany entrained air bubbles in it that it appears to be a foam-likematerial but the bubbles have been shown in the drawings as particulatebubbles.

FIG. 2 shows in more detail the structure of the primary bubblingremoving means 15 and the secondary bubble separating means or nozzlemeans 18. In this figure, conduit 14 is shown positioned to supplyliquid to the main bubble extracting means 15. Concentrically arrangedwithin the main or outer conduit 14 is the inner bubble receiving tubeor conduit 28, positioned to extend therein, as shown. It is preferablybevelled or chamfered on its inside free end as shown at 29 to provide asharp division point as at 30 between the material entering tube 28 andthat passing at the outside thereof.

Tube 28 is shown as pressed into and extending into the T-fixture 31 andterminates in a fiat shoulder 32. Fixture 31 is in turn assembled influid-tight relation in the end of tube 14, as shown, which has its wallthickened at that point to receive the end of fixture 31. For example,it may be threaded into the fixture and turned by means of the knurledcontrol knob 35. As will be appreciated, choke controls may be adjustedinwardly or outwardly (leftwardly or rightwardly with respect to FIG. 2)to seat or unseat on shoulder 32 to control the amount of liquid removedthrough tube 28 as desired. Return pipe 16 may thus be wholly orpartially connected to tube 28 by withdrawing the screw threaded controlmember 34 or pipe 16 can be cut off from tube 28 by advancing orscrewing in the control member 34. The main fiow of liquid materialby-passes the pipe 28 and fiows out through the connecting pipe 17 andinto the nozzle means or secondary bubble separating means 18, whichtakes the form of a curtain projecting nozzle block. Pipe 17 should belarge enough to avoid any substantial build-up of back pressure inconduit 14 and preferably at least as large as conduit 14 less the areaoccupied by the tube 28.

Conduits 14 and 28 will commonly take the form of tubes or pipes, etc.,particularly when liquid is being umped through a unit such as nozzle18. While conduits 14 and 28 are shown as cylindrical in cross-sectionand both of the same cross-sectional shape, this is not necessary,although preferred. Thus, it is contemplated that conduits ofrectangular or other cross-section may be used and that thecross-section of conduits 14 (or the main, large conduit) need not beprecisely the same in form as the cross-section of conduit 28 (thetake-off or smaller conduit) although such identity of form ispreferred. Likewise, when tubes are used, it is much preferred to placethe inner tube concentrically with respect to the outer tube, somedeparture is acceptable and it may be only substantially concentricallypositioned.

Nozzle block 18 is shown as suitably made up from two cooperatingportions designated 18R for the rear portion and 18F for the frontportion. The two portions are tightly secured together in any suitablemanner as by multiple closely spaced cap screws 36 as seen in FIG. 1.Each of the two portions 18R and 18E of nozzle block 18 has asemi-circular upper milled channel 37 which together form a cylindricalconduit or tube and into which the feed pipe 17 connects. Near each endof the channels 37 are the milled channels 38 which connect to lowermilled channels 39. Channels 38 and 39 also, in cooperation, formconduits. The bottom portions of milled channels 39 are relieved veryslightly so that when the two blocks are clamped tightly together as bythe screws 36, there is a thin slot 40 extending entirely across thebottom of the nozzle block 18 which slot is connected to the channels 39and initiates the film that is projected by the nozzle.

At each end of the conduit formed by channels 37 is placed a bubbletake-off tube, 41 and 41'. The bubble take-off tubes 41 and 41'terminate in chambers that are formed near the ends of the blocks anddesignated 42 and 42'. These chambers are milled in an oval pattern inorder to provide fiat outer sides 44, 44' against which the ends ofbubble take-off tubes 41, 41' may abut fiatly. This is a constructionexpedient and is not essential structure, it being necessary only thatthe tubes and conduits join. The inside ends of the bubble take-offtubes 41, 41' are also internally chamfered or bevelled to provide asharp edge as at 45 for separating the liquid entering the tube fromthat passing around its exterior. Edge 45 is similar to edge 29 for tube28.

Bubble take-off choke control members 46, 46' (similar to member 34) arescrews threaded into the ends of the nozzle block 18 for the purpose ofcontrolling the amount of material that flows through bubble take-offtubes 41, 41'. As in the case of the main bubble separating structurecontrol member 34, these choke screws 46, 46' are threaded into the endof the block and have knurled knobs to facilitate turning to advancetoward or retract the choke screws from the seats formed by block 18 atthe ends of channels 47, 47 which cooperate to form a conduitcommunicating with the inside of bubble take-off tubes 41, 41'. Thechannels 47, 47 also communicate with vertically milled passages 48, 48'(again cooperating to form conduits) from each of which a stream ofliquid having entrained air bubbles may be discharged in the samedirection as the film projected from the relieved portion 40 of nozzleblock 18. Note how the slot formed by relieved portions 40 and conduitsor passages formed by channels 48, 48 join at 40 and 40" respectively.

In FIG. 8 is shown a fragment of a modified form 15A of the primarybubble extracting unit 15 which is like the unit 15 in all respectsexcept that the main conduit 23 is comparable to conduit 14 is fluted onthe inside as at 33 to provide greater inside conduit surface. Thisincreases skin friction between the liquid and the main conduit whichimproves the bubble concentration in the center of the conduit 23,improving the efiiciency of bubble concentration entering bubbletake-off tube 43, similar to tube 28.

In the utilization of the foregoing structure, it has been noted that ifthe inner bubble take-off tube such as 28 or 45 is not concentric withits outer tube (14 in the case of tube 28 or the conduit formed bychannels 37 in the case of tube 41) the structure is less efiicient inremoving the entrained bubbles from the entire liquid flow through themain conduit. Eccentricity of even several thousandths of an inch, forexample, will reduce noticeably the efiiciency of the bubble take-oiftubes 48, 41, 41 and 43. Furthermore, particularly in the case of thenozzle means 18, this may be a problem because in operation there shouldbe a balance between the choke screw 46 and the choke screw 46'. With aslight eccentricity of either of the tubes 41 and 41, it is necessary tohave the choke controls opened farther than otherwise would benecessary, since the two controls should be opened about the same amountin order to balance the flow of material. The less efficient one must beopen substantially farther than the more efiicient one would need to bein order to actually remove all of the entrained air bubbles,

but to retain balance both must be opened excessively compared tooptimum conditions.

While a single separating structure such as that designated 15 willremove a very high percentage of the entrained bubbles in the liquid, itdoes not remove the desired amount of them without removing at the sametime a high percentage of material that could be useful as bubble-freeliquid.

According to the best of our knowledge and belief, there are threevariables which are the principle ones to take into consideration whendesigning or constructing a separating apparatus as described herein.The first is the viscosity of the fluid being used. In viscositieshaving a centipoise value of 5000 (hereafter abbreviated cp.) or more,conventional de-bubbling apparatus is not very effective and entrainedgas and liquid vapor bubbles will remain trapped and substantiallyimmovable in the fluid for a long period of time. Conventionalde-bubbling structures are necessarily very large and cumbersome evenwhen tie-bubbling liquids of viscosity as low as 2000 cp. When using thebubble extracting structure described herein, fluids of known viscosityof 20,000 cp. have been readily projected and recycled as visually clearfilms and similarly with fluids of viscosity estimated as high as 50,000cp.

The second major variable to consider in the size of the take-off tubein the conduit carrying the fluid from which the entrained gas bubblesare to be removed. In general, the more viscous the fluid, the smallerthe separating or take-off tube may be and still get effective removal.Generally also, the larger the take-off tube the more complete is theseparation achieved. Practically the take-off tube must be as small aspossible consistent with effective separation. The range suggested byexperiments to date is to have the inner or take-off tube of a diameterfrom A; to A of the main conduit diameter with /2 being a desirableratio when dealing with high viscosity fluids, i.e. 5000 cp. and up. Interms of capacity or tube cross section area, if it is preferred to usetubes of other than cylindrical form, the range is to 7 We believe thatvelocity of the fluid is the third major factor controlling theefiiciency of velocity gradient separation, since the greater thevelocity the more pronounced the difference between the rate of flow ofliquid at the center of the conduit and the flow adjacent the wall ofthe conduit. At the wall, the velocity is substantially zero. It isdesirable to have the difference in velocity or the velocity gradientchange as rapidly as possible from the wall surface to the center of theconduit. The velocity gradient will vary more rapidly as the averagevelocity of the material flowing in the conduit adjacent the take-01ftube increases. When dealing with liquids having a viscosity of from2000 to 20,000 cp. a velocity in the range of 300 to 450 feet per minuteis adequate to produce substantially total visual separation in twostages when the take-off tube is /2 the diameter of the conduit. Liquidsof lower viscosity would require greater velocities and/ or largertake-off tubes. The use to which material is to be put controls theviscosity, and in coating, the viscosity ranges from 2000 cp. when usingthe technique described and shown in FIGS. 4, 5 and 6, where a board anda fairly fiat object are being covered, to a film having a viscosity ofat least 10,000 cp. when encapsulating objects as shown in FIG. 9.

This method of separating discrete portions of immiscible matter, suchas bubbles of gas, from a liquid has the same effect as increasing thespecific gravity of the liquid in which the matter is entrained. At thesame time, the specific gravity of the/immiscible matter is notaffected. Accordingly, there is an increased tendency of the entrainedmatter to move toward the low pressure area in the structure of thisinvention as compared to movement toward the surface of the same liquidin a gravity settling tank. In a specific example, where liquid of 2000cp. viscosity was pumped at the rate of '7 gallons per minute through atube having a diameter of inch, it was calculated that the averagevelocity was 438 feet per minute. Velocity at the outside of the tube iszero and at the center of the tube twice average velocity or 876 feetper minute. The difference in velocity between the center of the tubeand its edge, only A inch distant, is thus 876 feet per minute. Thisvelocity in this size tube acting on a liquid of this viscoity wasfurther calculated to have the same effect as increasing the density ofthe liquid at least 127 times. Theoretically the increase may be greaterthan 127 times, and the figure 127 was used to be conservative. It canbe said, then, that bubbles of gas or other immiscible matter entrainedin the liquid would have 127 times greater force applied moving themtoward the lower pressure portion of the liquid than in the same liquidin a gravity settling tank. Another way of stating the same thing isthat for a given settling tank, liquid of the same viscosity would haveto have a specific gravity 127 times as great to produce the sameseparating action. When the effective or artificial specific gravity ofthe liquid is increased by a factor as great as this, natural gravityhas relatively small eifect on the discrete matter, such as gas bubbles,being separated so that the system will operate satisfactorily in anyattitude. Theoretically, however, most effective action will occur whenthe separation takes place in a vertical direction so that gravity haszero effect as far as the movement of the entrained immiscible matterthrough the liquid is concerned. While the structure was evolved toseparate entrained gas bubbles from liquids, the rate of pressure changeper unit of distance of the liquid is so tremendously enhanced by thistechnique that it is envisioned as a means for separating matter that isheavier than the liquid by inducing it to move to the center of therapidly flowing liquid in which immiscible matter is entrained. Itappears that almost any matter which is immiscible in the liquid can beseparated, if the viscosity and speed of the liquid and size of thetake-off tube are adequate with respect to the discrete pieces orbubbles which are to be removed.

When constructing units for separating air bubbles from liquids used inthe packaging techniques described herein, unit 15 is so constructed andarranged that the outside diameter of the bubble take-off tube 28 isfrom to and preferably approximately /2 the inside diameter of the mainflow conduit 14. Experience so far shows that more viscous liquids canemploy a smaller tube and less viscous a larger one. It is estimatedfrom visual inspection that with the illustrated arrangement of tubediameters, an average velocity range of about 300 to 450 feet perminute, a viscosity in the range of 2000 to 20,000 cp., and a very sharpcut-off edge 30 provided by the internal charnfer 29, the flow controlmember 35 may be adjusted to take-off between and 95 percent of theentrained bubbles in molten plastic without sacrificing excessivequantities of material that might be useful as clear liquid film formingsubstance. The second stage of the device is similarly effective inremoving 85-96 percent of the remaining entrained bubbles. For purposesof illustration, a hypothetical example in which each of the bubbleextracting units remove percent of the entrained bubbles would leave atotal of 1 percent of the original bubbles in the final film.

As a practical matter, however, the film that finally emerges from thenozzle slot 40 is visually free of bubbles. Furthermore, by turning thechoke screws 35, 46 and 46 in, the bubbles may be made to appear in thefilm, and .by backing off the control members 35, 36 and 36, the bubblesmay be made to disappear from the film or curtain 25.

It is also important to note that while the tubes 28, 41 and 41 could becha-m-fered on the outside as well as the inside and still produce asharply defined edge for separating the material with entrained bubblesand that which has none, to place the chamfer on the outside mightintroduce turbulence and bubbles into the otherwise smoothly flowingmaterial that is substantially free from bubbles. It is consideredpreferable, therefore, to have the chamfer an internal one rather thanan external one. For the same reason, bending of conduit 14 near tube 28or placing any structure within conduit 14 except tube 28 should beavoided to the extent possible. In fact, any substantial bending orimposition in the conduit of turbulence producing structure may destroythe bubble removing capacity of the structure at least in the sense ofproducing bubble-free liquid.

While all of the bubble removal from the film or curtain material couldbe accomplished prior to supplying it to nozzle slot 40, it is possibleto remove at least part of the material having entrained bubbles at thenozzle itself use the bubble containing material as a stabilizing columnat each margin of the film or curtain 25. Even with these columns ofbubbles helping to hold the curtain edge from drawing together, theedges of the curtain or film slant inwardly slightly. This is a naturalresult of the molten material tending to contract under the influence ofsurface tension and cooling. This contracting of the film both reducesthe width of the curtain the farther it gets from the nozzle slot 40 andcauses it to thicken.

If the curtain film 25 were projected from nozzle 40 without the latterbeing in contact with the bubble columns, it would contract or divergeinwardly at the edges substantially as shown by the broken lines 50.However, when the film is projected to contact with the columns ofmaterial having entrained air, the contracting tendency is counteractedin part. The columns are substantially thicker in section than the filmand also are cylindrical in pattern. For these reasons, surface tensionin the liquid columns will only reduce the diameter of the cylindricalformation, and the columns tend to project straight downwardly. Being incontact with the edge of the curtain, they tend to hold the curtain in astretched condition and produce a double desired effect. In the firstplace, they increase the breadth of the usable portion of the curtainsubstantially and in the second place they tend to retain the curtain ata uniform thickness throughout its useful projection. Thus, theentrained air bubble separating structure at the nozzle itself servesthe dual important functions of extracting the last traces of airbubbles from the curtain material and at the same time provide a curtainwith stabilizing column at each marginal edge. Ball type chains havealso been found to produce the same result if secured at the ends of thenozzle slot 40. These balls act on film 25 in exactly the same way thatbubble columns 26 do.

Reference to FIGS. and 6, in cooperation with FIG. 4, illustrates anarticle being coated by the foregoing structure. In those figures, andparticularly in FIG. 4 in the first instance, an object 51 such as anysuitable piece of merchandise to be packaged is shown lying on a treatedbacking card 52 to which the film will adhere, which serves as a supportfor the object and which also may contain advertising and salesmaterial. The treatment applied to the board to permit adherence of themolten plastic forms no part of this invention per se, hence need not bedescribed here. The speeds of operation of belts 20 and 21 are withinthe range of /2 to 6 times the rate of flow of the film 19 beingprojected by the nozzle block 18.

As shown in FIG. 5, the conveyor 20 has projected the object 51 wellinto the film or curtain 25 which is shown extending over the card 52 inthe front of the object 51. As illustrated here, it appears to be a filmcovering the object in only two dimensions. In actual fact, of course,the material flows over the sides of the object 51 and engages the cardon the marginal edges, as shown at the front of the card 52 (see alsoFIG. 7). In FIG. 6, the initial object 51 and its card 52 have beenprojected entirely through curtain 25 and is covered with a filmconsisting of a portion of curtain 25 and designated 25F.

At the same instant, a second object 51' is about to be projected on itscard 52' into the curtain 25. Between objects and also at the marginaledges of any object will be excess curtain material and the bubblecolumns 26 which of course fall into and are caught by return trough 22.Pipe 24 conducts material in trough 22 back to reservoir 10.

When a structure such as that illustrated here is used in conjunctionwith material such as polyethylene, which must be heated to a relativelyhigh temperature in order to remain in a molten state, the entiremechanism or desired portions thereof are heated by means of anysuitable heating structure such as jacketing 53 surrounding all of thestructure except return tube 16 which has a heating pipe 53' connectedinto the main jacket 53 through which heated liquid is pumped via aninlet 54 and an outlet 54'. Thus a suitable heating arrangement for thecircuit is provided to keep resin in it in a liquid state. As theheating structure may be conventional, it is neither shown nor describedin more detail, since it forms no part of this invention per se.

In FIG. 9 is seen a portion of the nozzle 55 substantially identical tonozzle 18, discharging a film or curtain 56 through which an object suchas a pen represented at 57 is projected by suitable structure, or byhand. The projection is in the direction shown by the large arrow andthe orientation of the pen 57 to the film 56 is endwise. As the pen isprojected through the curtain as by being propelled from any suitableconveyor and allowed a free fall through the curtain generally in thedirection of the arrow, the pen is completely encapsulated by thefalling curtain and comes out as seen at the left where film 58 forms aseamless, unbroken sheath around the pen. This type of packagingrequires a film curtain of considerable strength and requires a materialhaving a viscosity of 10,000 cp. or more. The speed of the pen throughthe curtain is preferably within the range of to 6 times the linear fallof the curtain though experi ments suggest that higher speeds may beacceptable with stronger films than those presently available.

It is apparent that many modifications and variations of this inventionas hereinbefore set forth may be made without departing from the spiritand scope thereof. The specific embodiments described are given by wayof example only and the invention is limited only by the terms of theappended claims.

We claim:

1. A nozzle means for creating a substantially bubblefree curtain of aliquid comprising, a nozzle body memher, a conduit communicatingtherewith, means within said nozzle body member for conducting liquidfrom said conduit to a thin continuous substantially horizontal channelmeans having an open bottom, said nozzle body member having verticalchambers extending to the ends of said thin channel means, and saidnozzlemeans for cluding velocity gradient bubble separation means fordelivering separated liquid containing entrained gas bubbles to saidvertical chambers.

2. A nozzle for creating a bubble-free curtain of a liquid comprising, ablock member, an upper channel in said block member, a conduitcommunicating with said block member upper channel, a lower channel insaid block member, vertical channels connecting the upper and lowerchannels in said block member, a thin continuous passagewaycommunicating between the lower edge of said block member and said lowerchannel, vertical chambers extending from the upper inside of said blockmember to the ends of said thin channel, tube means extending from saidvertical chambers into said upper channel and beyond said verticalchannels and substantially concentrically into the ends of said upperchannel, said tubes having a capacity in the range of to A of said upperchannel, and passageways in said block member communicating between saidtubes and said 11 12 vertical chamber, said upper channel beingsubstantially 3,117,342 1/1964 Koppehele 18----12 free from turbulenceproducing structure. 3,345,803 10/ 1967 Smith 55-55 3. The structure ofclaim 2 in which said upper channel and tubes are cylindrical and saidtubes are internally HENSON WOOD, y Examlner chamfered and have outsidediameters of /6 and the 5 LOVE, Assistant Examiner inside diameter ofsaid upper channel.

US. Cl. X.R. References Cited 239413; 1 12 UNITED STATES PATENTS2,921,548 1/1960 Kane 239-597 x 10

